JPS6386973A - Light sensitive pickcell with exposure blocking device - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a photosensitive array, and more particularly an integrated array of thin-film photoelectric elements, and a photosensitive array that transmits the photoelectric signals emitted by said elements with minimal cross-talk. )
Concerns an improved addressing scheme for reading.

Background of the Invention ■ To understand the present invention, [image or optical scanning device]
is defined as a device that includes one or more photoelectrically responsive circuits or elements arranged to optically scan a pattern of data and produce a signal representative thereof.

Optical image scanning devices convert patterns of data into electrical signals that can be applied downstream to subsequent processing, storage, or display devices. Image scanning equipment includes facsimile transmitter, copy layer, computer input terminal, CAD-CA
It is built into the M device, etc. In addition, image scanning devices are also used in manufacturing processes to inspect the surfaces of materials such as plywood, fibers, and flexures. A typical image scanning device includes one or more charge-responsive circuits arranged to simultaneously or sequentially address various portions of the surface to be scanned.

Several attempts are currently being made to manufacture image scanning devices. Charge-coupled devices (CCDs) provide the basis for one such effort. (10) D is a solid-state device, typically made of solid silicon, containing a plurality of photoelectrically responsive circuits with individual pixels bonded therein.

(10) D has a high degree of photoconductivity and can provide high resolution. However, (10)D has relatively small dimensions. A typical (10)D array is approximately 1 inch long, and the largest (10)D currently manufactured is approximately 3-4 inches long. These dimensional constraints impose a mlJ limit on the effectiveness of (10)D in the scanning device. (10)
If an information pattern with dimensions larger than D is to be scanned, an optical system must be used to project the information pattern in reduced size onto the surface of (10)D. Apart from being expensive and bulky, this type of optical system is (10)D
will effectively reduce the resolution of the image.

Thin film devices are another approach to manufacturing image scanning devices. Thin film devices may be formed by depositing layers of suitable amorphous semiconductor materials onto various substrates. By appropriately patterning these layers, a variety of device configurations can be realized.

The term "amorphous" as used herein includes all materials or alloys that have short-range or intermediate-range order or contain crystalline inclusions, but also have angular disorder. The M1 term "microcrystalline" also means that the volume fraction of crystalline inclusions is greater than a threshold value, resulting in substantial changes in some key parameters such as conductivity, bandgap, and absorption constant.

By glow discharge or other deposition methods, λ? IFJ amorphous silicon, large area germanium or silicon
A germanium alloy can be fabricated, which has a low concentration of localized states in the energy gap and high performance electronic properties.

Thin-film alloys can be easily fabricated over large areas by large-α production processes, and are therefore one of the
ff: Can be manufactured universally. The use of large scale arrays of this type provides savings in cost, production scale and processing steps, and eliminates the need for complex optical systems. In addition,
Since the thin film Binsa array is manufactured to approximately the same size as the object to be scanned, the relatively high W? Image power is achieved without the need to use high resolution photolithographic processing steps. Therefore, it can be seen that thin film photovoltaic arrays have great effectiveness in manufacturing image scanning devices.

A typical film image scanning device includes an array of photoresponsive circuits, each circuit including a photoelectric element adapted to provide an electrical signal corresponding to Φ of light incident thereon.

Obviously, using a single element to scan a large surface area would be a waste of time. Therefore, linear or two-dimensional arrays of elements are commonly used. If this type of array is used, each optoelectronic circuit of the array must also include a blocking element, such as a diode or transistor. The blocking elements facilitate addressing of the various charging elements within the matrix by preventing current from flowing through undesired paths within the matrix of the array. In this way, you can also use a blocking device.
Eliminates crosstalk that would otherwise degrade the signal produced by the photoconcentrator.

In the use of prior photosensitive arrays, several problems arose due to the generation of charge carrier pairs within the blocking element due to the absorption of incident light. Light with an energy greater than the bandgap of the semiconductor material from which the blocking element is fabricated can create electron-hole pairs in that material. If there is a magnetic field across a semiconductor material, what about light? 171
The child-hole pairs are separated, thereby producing a Ti stream. Prior to this, this kind of illumination of blocking elements was
It was possible to create a current flow that effectively became a source of "noise". This "noise" disappeared or otherwise degraded the signal produced by the sensitivity of the photoelectric element. For this reason, it has hitherto been necessary to optically shield blocking elements to prevent illumination.

This type of masking has been performed by depositing relatively thick, opaque metal or other layers over the blocking elements, or by using tape or other shields to avoid illumination.

This approach is clearly far from satisfactory insofar as it requires additional processing steps. For example, the deposition of metal layers requires great care if short circuits are to be avoided. The use of separately applied tape or other masking elements should provide sufficient room for the placement of the masking element so that the blocking element is not exposed to light fft.
It is necessary to place it relatively far away from the 7R child. Such remote placement wastes space and reduces resolution;
Furthermore, they require the use of relatively long connectors between them, and such connectors add undesirable capacitance to the circuit.

Therefore, it eliminates the need to cover the blocking element from the incident beam, and prevents the scale masking process from harming the underlying adjacent element, increasing cost and wasting processing time and materials.
It will be appreciated that it is desirable to avoid disadvantageously increasing the size and electrical capacitance of the photosensitive pixels.

Accordingly, the present invention provides an apparatus for manufacturing photovoltaic responsive circuits that include a photovoltaic element and a blocking element, without the need for shielding the blocking element from incident light.

These and other advantages of the invention are described in the Summary of the Invention, the Drawings,
It will be readily apparent from the description of the drawings and the claims.

Disclosed herein is a circuit for providing a detectable signal in response to the amount of incident light.

The circuit includes an optoelectronic device including at least first and second electrodes, and further includes an element for selectively passing a blocking current through at least a portion of the circuit, the device including at least the first and second electrodes. (a first electrode of the optoelectronic element and a first electrode of the blocking element being electrically interconnected, while a second electrode of the optoelectronic element and a second electrode of the blocking element are held at a substantially common potential); , '7,
Therefore, no detectable signal is consumed by the carrier pairs photoelectrically generated by the current blocking element.

The photoelectric element can be a photoresistor, a phototransistor or a photodiode. When the photovoltaic element takes the form of a photodiode, it incorporates oppositely doped layers made of thin film semiconductor alloy material, between which the virtually intrinsic semiconductor alloy material forms p-1-n type bottoms. arranged to form a diode. In a most preferred embodiment, the semiconductor layer of the photodiode is formed primarily from a material selected from the group consisting of an amorphous silicon alloy material, an amorphous germanium alloy material, and an amorphous silicon:germanium alloy material.

The photoelectric element may include a plurality of p-1-n type photodiodes stacked in optical and electrical series relationship.

A preferred embodiment of the blocking element includes a layer of photoresponsive semiconductor alloy material capable of generating charge carrier pairs in response to absorption of incident light. The blocking element may be a transistor or a diode. When the blocking element takes the form of a diode, it may include a pair of layers of oppositely doped thin film semiconductor alloy material V, between which there is an intrinsic A layer of semiconductor alloy material is disposed. The p-1-n type diode is formed primarily from a layer of a semi-eta alloy material selected from the group consisting of an amorphous silicon alloy material, an amorphous germanium alloy material, and an amorphous silicon: germanium alloy material. The diode consists of a plurality of p-t-
The total weight of the n-type diodes is 1g. The diode may also take the form of a Schottky barrier. However, the blocking means are virtually not covered from the incident light.

In a preferred embodiment, a low impedance current amplifier is applied to keep the second voltage of the optoelectronic element and the second electrode of the current blocking means at substantially equal potentials, such as O volts. The photoelectric element is preferably a photodiode with an anode and a cathode, and the blocking element is preferably a blocking diode with an anode and a cathode, so that when the photodiode is exposed to light, an electrical signal in the form of photoelectric carrier pairs is accumulated on the conductor. , the anode of the photodiode and the anode of the blocking diode are electrically interconnected by the conductor such that the anode of the photodiode and the anode of the blocking diode are held at substantially the same potential during exposure of the circuit. .

By using a plurality of photodiodes and a plurality of operatively arranged coupling blocking diodes,
The circuitry should provide a plurality of electrical signals corresponding to the characteristics of the incident light (and can be used to provide a tailored pixel array).

The pixel array may be linear or two-dimensional.

In a preferred embodiment, a support substrate is provided with a conductive surface of at least 1 vA. A photodiode and a blocking diode are spaced apart on a conductive surface having a cathode electrically coupled to the conductive surface to establish electrical coupling therebetween.

The circuit further includes a first transparent conductor disposed above the anode of the photodiode, a second transparent conductor disposed above the anode of the blocking diode, and a portion of the first transparent conductor and a second transparent conductor disposed above the anode of the blocking diode.
It includes a conductor in contact with a portion of the transparent conductor.

Further included within the scope of the invention are current blocking devices for use in photoresponsive circuits, said circuits comprising photovoltaic elements;
It is also envisaged that it will be adapted to provide and store a detectable signal corresponding to m of light incident thereon. The circuit further includes an element for selectively blocking current passing therethrough.

The blocking element includes in combination: That is to say, it is the surface on said circuit which is not actually covered by one beam of light, so that its photovoltaic area can at least partially access said beam. Furthermore, specific examples of this photoelectric element may be a photoresistor, a phototransistor, a photodiode. It is contemplated that both the blocking optoelectronic element and the blocking element are formed from one or more triplets of p-1-n@ type layers of semiconductor alloy material. In addition, the second electrode of the photoelectric element and the second electrode of the current blocking element are also included. The δ voltages are held at a substantially equal potential of approximately 0 volts by a low impedance current amplifier while the first voltage is electrically interconnected. By using a plurality of coupled photodiodes and blocking diodes operatively arranged to form an array, the electrical signals generated by said array will correspond to the light emitted from the image sensed by the image sensor. .

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is best understood with reference to the drawings. Figures 1 and 1B illustrate a preferred method and circuit for reading signals generated by individual photosensitive circuits while the array of photosensitive pixels is in motion.

As used herein, the term "photosensitive circuit" or "photoresponsive circuit" refers to that portion of a photosensitive array associated with an individual pixel, typically providing a detectable signal in response to absorption of incident light. a blocking element for selectively limiting current flow through portions of the circuit; and associated addressing means. Figure 1Δ shows a photosensitive pixel 10 for receiving incident light 12;
The figure shows a photosensitive pixel 1 read out by an output amplifier 14.
Indicates 0. As can be seen with reference to Figures 1A and 1B,
Photosensitive pixel 10 includes two diodes, a blocking diode 16 and a photodiode 18 electrically connected in a back-to-back configuration. For convenience in explaining the operation of the photosensitive pixel 10, the internal capacitances 2o and 22 of the diodes 16 and 18 are designated as 1 Δ and 1 Δ, respectively.
It is shown as a separate part in Figure B. The anodes of diodes 16 and 18 are coupled to a common point or node 24.

The cathode of photodiode 18 is coupled to output node 26;
The cathode of blocking diode 16 is coupled to input node 28 . Both diodes 16 and 18 are preferably constructed and operated to produce currents I8 and 1, respectively, which are exposed to light during operation. Each diode is therefore designed as a miniature solar cell, the energy output per scanning period being proportional to the total amount of incident light during the scanning period.

Because the photosensitive pixel 10 effectively integrates the total charge produced by the incident light over each scan period, it is much more sensitive than prior art photosensitive elements that simply measure the incident light on an instantaneous basis. Signal amplifier 14 is for producing an amplified output signal that is proportional to the current passing through node 26 when photosensitive pixel 10 is read.

It is an important feature of the invention that the voltages at nodes 26 and 28 are held at substantially the same value during the sensitive (ie, non-read) portion of the cycle. This prevents the photoelectric current that occurs during the illumination of the blocking diode 16 from dissipating. Otherwise, the photocurrent produced by photodiode 18 and stored at node 24 will be degraded. Therefore, the blocking diode 16 does not need to be masked from the incident light, thus simplifying the pixel design and processing steps.

The voltage at node 26 between photodiode 18 and amplifier 14 and the voltage at input node 28 are preferably held at zero volts whenever photosensitive pixel 10 is not being read as shown in FIG. Voltage values may be used as well.

Therefore, when diodes 16 and 18 are exposed as shown in FIG. becomes less negative than the negative voltage placed at , and at the end the photosensitive pixel 10 is read.

As shown in FIG. 1B, incident light 1 impinging on the photosensitive pixel 10
2, the voltage at input node 28 is reduced from, for example, zero volts to 15 volts. The blocking diode 16 is thus 5f
current passes until the voltage at node 24 is approximately equal to 15 volts.

In fact, the internal voltage of diode 16 is at node 24
can be prevented from reaching the voltage applied to input node 28. This change in voltage at node 24 is
It is followed by a current indicated by dashed line 30.

Photodiode 18 is now biased and reversed, experiencing a final reverse bias voltage of approximately 15 volts according to the time of the read pulse.

Sometimes this reverse current 30 is passed through the internal key 1 of the photodiode 28.
? It is also useful to think of it as passing through the capacitor 22, thus applying 5 volts to the capacitor 22. On the other hand, the blocking diode 16 is forward biased and therefore its internal capacitance 20
, ie, the voltage 20 across internal capacitance 20 is equal to the final forward voltage drop achieved across diode 16. Current 30 across node 26 is amplified by signal amplifier 14 resulting in an amplified current IA through output node 32 and photosensitive pixel 1.
is proportional to the intensity of light received during a current scan period by 0.

At the end of the scan pulse, the voltage at input node 28 returns to zero volts and the voltage at node 24 remains at approximately -5 volts as long as the photosensitive pixel 10 receives no further incident light. Finally, node 26 returns to zero volts and the circuit is reset to sensitive mode.

Figures 2A-2C collectively illustrate the time response of the output of a photosensitive pixel, e.g. 10, to changes in light intensity.
FIG. 3 is a timing diagram of two waveforms. The first waveform to FIG. 2 shows a 15 volt drive pulse placed on input 28 of FIG. 1B. For those skilled in the art, the time interval length and frame time are:
It can be seen that there are 1q changes to adjust for the difference in time response and the number of photosensitive pixels to be addressed.

The waveforms shown in FIG. 2B are triggered at node 24 in the photosensitive imager 10 of FIG. The corresponding voltage ■, which occurs when the next encounter occurs, is shown. As shown, the voltage at node 24, V, increases from approximately 15 volts to approximately zero volts when a fully open segment of the image is encountered. At the end of this first charging cycle, input pulse 34a causes this voltage to return from approximately zero volts to 15 volts. Therefore,
The output current signal shown in FIG. 2C measures the current passing through blocking diode 16.

If the image encountered in the next scan period or frame is dark, no appreciable photocurrent will be generated and therefore the junction node 24 will
The voltage ■J does not change even if the read pulse 34b appears. If the image consists of a segment producing an intermediate brightness level located between dark and fully open, the photocurrent generated will have an intermediate value of 0 and 15 volts, and the photocurrent at node 24 will have an intermediate value of 0 and 15 volts. Change occurs.Next read pulse 3A
In c, only a moderate voltage change occurs at node 24, and a moderate output occurs at node 32, as shown correspondingly in FIG. 2C.

The readout scheme described above has significant advantages over other readout techniques known to those skilled in the art. One such advantage is that electrical crosstalk due to undesirable current flow through other elements in electrical communication is virtually eliminated. The reason for this can be explained with reference to FIG. In the figure, for clarity and ease of discussion, a prior art linear array is shown consisting of two photosensitive circuits or groups 36a and 36b, each having two photosensitive elements. When connected as shown, amplifier 14a is operative to sense the current produced by either photosensitive pixels 10a of group 36a or photosensitive pixels 10b of group 36b, depending on which group is being interrogated. In practice, the total current sensed by amplifier 14a when reading photosensitive element 10a is the sum of the current 38 from photosensitive element 10a and the additional leakage current 40 passing through pixels 10b and 10c of unselected group 36b. ′a passing through multiple current paths
i current and the current passing through other pixels 10d in the selected group 36a in the path indicated by the darker break Q40. This type of current is caused by variations in the operating characteristics between photosensitive pixels 10 and the fact that output line 46 is not held at zero volts. In large photosensitive arrays with groups of dozens or even hundreds of pixels, this unwanted crosstalk current can negatively affect the read viscosity of individual photosensitive pixels 10. However, in the present invention, the input line 46 and the output line 4
4 are held at virtually the same potential and there is no negative current. The current required to recharge each pixel 10 is therefore detected only by its corresponding amplifier 14.

FIG. 4 is a simplified schematic illustration of a preferred addressing and reading method for the photosensitive pixel 10 of the present invention. As shown, all output lines 46 as well as all input lines 44 are held at zero volts, thus eliminating unwanted leakage currents. Since each photosensitive pixel 10 in an unaddressed group is at the same voltage, there is no current through these unaddressed pixels. Crosstalk is therefore effectively prevented since there is no effective path, ie, a path through which the cross-[hake currents] can be routed, that has a voltage drop. Those skilled in the art will appreciate that this preferred method of reading arrays, such as linear arrays of photosensitive pixels, also obviates the need to precisely match the I-V characteristic values of all blocking diodes and all photodiodes. be understood.

FIG. 5 is a top view of the output line 46 and input line 44 coupled to two adjacent photosensitive pixels 10.

FIG. 6 is a side cross-sectional view corresponding to one of the photosensitive pixels 10 taken along line 6--6 of FIG. 5 and 6 show that the photosensitive pixel 10, the input line 44 and the output line 46 are deposited with thin film semiconductor alloy materials, insulators and conductive lines;
It is further illustrated that the structure 1q can be formed as a single integrated structure using well-known techniques for patterning using conventional photolithography techniques. As shown in FIG. 5, the photosensitive array may include a plurality of photosensitive pixels 10 arranged parallel to each other and spaced adjacent to each other. 1
For each array, the approximate dimensions of the same photosensitive pixel 10 may be as follows. The center-to-center distance between adjacent pixels 10 in any direction may be approximately 60 microns. Photodiode 18 may be formed as a square with approximately 42 microns on each side, and roughly blocking diode 16 may be formed as a square with approximately 24 microns on each side. The blocking diode 18 can be placed on top of a suitable conductive base 5o of approximately 30 microns square, which serves as one of its electrodes. The photodiode 18, on the other hand, has a suitable conductive base 52 approximately 52 microns square.
This base can be placed on one of its electrodes.
move as one. Conductive bases 50 and 52 are preferably interconnected by a conductive connector 54. The total longitudinal length of photosensitive pixel 10 may be approximately 250 microns. Iode 18 for each photodiode 18
It can be made by increasing the dimensions of. However, as can be easily seen from FIG. 5, increasing the size of each photodiode will affect the resolution of the array. Additionally, if the blocking diode is made too large compared to the photodiode, extra capacitance is added to the circuit,
This capacitance will be detrimental to its operation. It has therefore been found desirable to have the photodiode have an area that is at least 5 times, preferably 10 times larger than the area of the blocking diode.

FIG. 6 shows that a photosensitive pixel 10 is formed on an insulating substrate 56, which substrate is preferably a Corning.
Q) 7059 glass, but indicates that it may be formed from other suitable materials, such as stainless steel coated with an insulating layer. At the top of the substrate 56 is a bottom full flexure layer 58.
is formed, which may be chrome, and said layer 5
8 forms a patterned metal layer on the underside of each photosensitive pixel 10, which is patterned using photolithography using conventional techniques to simultaneously form input lines 44 and output lines 46. patterned metal layer 58
form conductive bases 50 and 52, which serve as one of the electrodes for diodes 16 and 18, respectively.

Metal layer 58 also forms a conductive connector 54 interconnecting the two bases. A layer of N-1-P semiconductor alloy material 60 is then deposited over bases 50 and 52 to form the photosensitive portions of diodes 16 and 18.

Disposed on each layer 60 is a separate top contact 62, said top contact preferably being made of indium tin oxide (ITO).
) made from transparent conductive oxides such as

An insulating layer 64 is then deposited and patterned to isolate conductive lines or traces 68 and 70 from electrical communication with other portions of the array except where desired. For example, conductive line 68 contacts input line 44 through path 72 and is electrically connected through path 74 to contact 62 of diode 1 .

Similarly, conductive line 70 passes through passage 76 to output line 46.
in contact with the top contact 6 of the photodiode 18 in the passage 78.
Make an electrical connection with 2.

4' electrical connectors 54 on the bottom conductive layer 58 provide electrical connection to the photodiodes 16 and 18 in a back-to-back manner, while top metal conductive traces 68 and 70 connect the photodiodes 16 and 18 to the bottom connection layer 5.
An electrical connection is provided to the electrodes of diodes 16 and 18 opposite to 8.

In prior art structures, it is not necessary to cover the blocking diode 70 from the incident light, however, in the present invention to prevent the generation of currents that would add noise to the output of the conductive circuit and degrade sensitivity.

As shown by the above description, the present invention provides a novel addressing scheme that does not require shading of blocking elements and makes it possible to fabricate photosensitive arrays with less electrical crosstalk between pixels.

Although preferred embodiments of the invention have been described in detail, it should be understood that various modifications and changes can be made by those skilled in the art without departing from the spirit of the invention. For example, elements other than diodes may be replaced by blocking and photoelectric elements. The principle is that it is equally applicable to circuits including thin film transistors, crystal transistors and the like. The claims defining the scope of the invention include all equivalents thereof.

[Brief explanation of the drawing]

1A and 1B are schematic diagrams illustrating a preferred method of reading signals photoelectrically generated by the photosensitive pixels of the present invention;
FIG. 3 is a schematic diagram illustrating the electrical crosstalk that occurs between adjacent groups of conventional photosensitive pixels; FIG. 5 is a schematic diagram illustrating a technique for reading photosensitive pixels without crosstalk; FIG. FIG. 3 is a lateral side view of one of the individual photosensitive pixels shown in FIG. 10... Photosensitive pixel (photoelectric response circuit) B → Screaming - 1. 14...Output amplifier, 16...Pro-lagging diode, 18...Photodiode (
Photoelectric element), 20, 22...Internal capacitance, 24, 2G. 28...Node. F/σ3 νResponse Ghost F/σ4

Claims (15)

[Claims] (1) A circuit for providing a detectable signal corresponding to the amount of light incident on a photosensitive pixel, the circuit including a photoelectric element including at least first and second electrodes, and a current flowing through at least a portion of the circuit. means for selectively blocking the optoelectronic element, the first electrode including at least a first and second electrode, the first electrode being electrically interconnected with a first electrode of the optoelectronic element; a second electrode and means for effectively holding the second electrode of the blocking means at a common potential, whereby the accumulated detectable signal is a carrier pair photoelectrically produced by the unmasked current blocking means. circuits that are not consumed by. 2. The circuit of claim 1, wherein the photoelectric element is a photodiode comprising a reverse doped layer formed of a thin film semiconductor alloy material. (3) The photodiode further includes a layer formed of a substantially intrinsic amorphous semiconductor alloy material interposed between the counterdoped layers to form a pin photodiode. The circuit according to paragraph 2. 4. The circuit of claim 1, wherein said blocking means comprises a layer of photovoltaically responsive semiconductor alloy material capable of generating charge carrier pairs in response to absorption of incident light. (5) The blocking means is made of a thin film semiconductor alloy material.
2. The circuit of claim 1, being a diode comprising a pair of oppositely doped layers. (6) The blocking means is a diode comprising a layer of intrinsic semiconductor alloy material interposed between the counter-doped layers to provide a pin diode. circuit. 7. The circuit of claim 1, wherein said blocking means is substantially unshielded from incident light. (8) The circuit according to claim 1, wherein the potential holding means is configured to hold a potential of approximately 0 volts. (9) The circuit according to claim 1, wherein the potential holding means includes a low impedance current amplifier. (10) the photoelectric element is a photodiode with an anode and a cathode; the blocking means is a blocking diode with an anode and a cathode; the cathodes of the two diodes receive an electrical signal in the form of a photoelectric carrier pair during exposure of the photodiode; are electrically interconnected by said conductor such that the photodiode anode and the blocking diode anode are held at substantially similar potentials during exposure of the circuit. The circuit according to claim 1. (11) further comprising a plurality of photodiodes and a plurality of coupled blocking diodes operatively arranged for use as an array of photosensitive pixels, each pixel configured to provide an electrical signal corresponding to the amount of light incident thereon; 11. The circuit according to claim 10. (12) A current blocking device for use in a photosensitive pixel, the circuit including a photosensitive device configured to provide a detectable signal responsive to the amount of light incident on the photosensitive pixel; A blocking element comprising a photodiode including a photoelectric region capable of generating charge carriers in response to incident light, said photodiode being at least partially unshielded from said incident light. 13. The device of claim 12, further comprising means for maintaining the second electrode of the optoelectronic device and the second electrode of the current blocking device at substantially equal potential. (14) The device according to claim 13, wherein the potential holding means is configured to hold a potential of approximately 0 volts. (15) The photoelectric element is a photodiode having an anode and a cathode, and the blocking diode has an anode and a cathode, and the cathodes of the two diodes are such that an electric signal in the form of photoelectric carrier pairs is transmitted onto the conductor during exposure of the photodiode. and wherein the anode of the photodiode and the anode of the blocking diode are held at substantially similar potentials during exposure of the circuit. The device according to range 12.